1. Field of the Invention
The present invention generally relates to non-magnetic one-component developers used in electrophotographic image forming apparatuses such as electrophotographic printers and copying machines. More particularly, the present invention relates to a non-magnetic one-component developer that can restrict the welding to peripheral equipment during a printing operation over a long period of time, and can prevent burring in printing and a decrease in image density.
2. Description of the Related Art
Conventionally, an electrophotographic image forming apparatus forms a latent image on a photosensitive drum by giving uniform electrostatic charges and then emitting light onto the surface of the photosensitive drum as a latent image carrier. The latent image is then materialized by the use of a developer containing coloring particles called toner, thereby forming a toner image. This toner image is then transferred and fixed onto a recording medium such as paper or transparent film.
To supply a developer onto the photosensitive drum in an image forming apparatus, a developing roller for transporting the developer is disposed adjacent to the photosensitive drum. This developing roller is provided with a blade for restricting the developer within a predetermined thickness.
The developer described above does not include carriers and is used for development only with toner particles. Such a developing technique is called a one-component developing technique. There are two types of toners used in the one-component developing technique: one is magnetic toner that has magnetism, and the other is non-magnetic toner that does not have magnetism. It is easier to simplify the structure of apparatus by a non-magnetic one-component developing technique using the non-magnetic toner. For this reason, intensive studies on the non-magnetic toner are being made these days.
However, there is a problem that the non-magnetic one-component developer often causes welding and adhesion to a blade of a developing apparatus. During a printing operation over a long period of time, the non-magnetic one-component developer is repeatedly brought into contact with the blade. As a result, the non-magnetic one-component developer adheres to the blade. Sometimes, the non-magnetic one-component developer even turns into lumps on the surface of the blade, and hinders the formation of a toner image on the developing roller. These lumps of the non-magnetic one-component developer cause white lines and unevenness in image density.
In order to solve the welding problem, many solutions have been suggested. For instance, Japanese Laid-Open Patent Application No. 4-368959 discloses a developer containing prescribed styrene-acrylic resin and propylene-1-butene copolymer. Japanese Laid-Open Patent Application No. 5-61245 discloses the use of positively charged additive particles. Japanese Laid-Open Patent Application No. 4-145448 discloses a technique of externally adding improved hydrophobic silica. Japanese Laid-Open Patent Application 5-107804 discloses a developer using a polymer containing acrylic acid nitrile. Japanese Laid-Open Patent Application No. 5-142857 discloses a toner having special surface properties.
The prior arts disclosed in the above references all concern improvements of the toner particles or the fine particles attached to the surface (hereinafter referred to as an xe2x80x9cexternal additivexe2x80x9d) of each toner particle so as to control the charging properties and fluidity of the toner particles. In other words, all the inventions disclosed in the above references are to obtain a non-magnetic one-component developer that solves the welding problem.
However, all the prior arts have not succeeded to eliminate the welding problem completely. In order to solve the welding problem, the inventors of the present invention conducted a long-time printing test on a conventional non-magnetic one-component developer so as to find out the causes of the welding problem. More specifically, the elements constituting the welded substance adhering to the blade ware analyzed in great detail. Based on the results of the elemental analysis, it was found that the welded substance adhering to the blade contained more elements originating from the external additive than the non-magnetic one-component developer did. Although the cause of this is not clear, it is thought that many of the external additive particles were detached from the toner particles (those detached external additive particles will be hereinafter referred to as xe2x80x9cfree external additivexe2x80x9d). The inventors assumed that it was the free external additive that caused adhesion to the blade. On this assumption, the inventors aimed to reduce the amount of free external additive that is detached from the toner particles, and have developed the present invention.
In order to make a more detailed analysis of the adhering substance, the inventors employed an emission analysis method using fusion coupling plasma. Examples of conventional quantifying techniques for free external additive particles include a technique of quantifying the amount of free external additive by subjecting toners dispersed in water to ultrasonic wave of predetermined power (disclosed in Japanese Laid-Open Patent Application No. 9-176232), and a technique of separating the external additive by performing air separation (disclosed in Japanese Laid-Open Patent Application No. 6-25836). According to either of those analyzing techniques, the external additive is forcibly separated from the surface of each toner particle. However, actual analysis of the condition of the non-magnetic one-component developer used in an image forming apparatus has not been made yet.
In view of this, the inventors of the present invention employed an emission analysis method using fusion coupling plasma, so as to analyze the developer having a condition closer to the actual condition of actual image formation. Based on the results of the emission analysis method, a more preferable non-magnetic one-component developer was obtained.
A general object of the present invention is to provide non-magnetic one-component developers in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a non-magnetic one-component developer of an electrophotographic image forming apparatus that does not cause welding to a blade during a printing operation over a long period of time and accordingly enables excellent image formation. The present invention is also to provide a developing apparatus using the non-magnetic one-component developer.
The above objects of the present invention are achieved by a non-magnetic one-component developer comprising:
toner particles; and
an external additive containing inorganic particles that adhere to a surface of each of the toner particles,
wherein, in accordance with an emission analysis method utilizing fusion coupling plasma, a proportion of free external additive particles that is determined by the number of detection events, in which light only from elements of the external additive is detected, is 9% or less by number.
With this non-magnetic one-component developer, an image having neither white lines nor uneven image density can be obtained, even after a long-time printing operation. The welding can be effectively prevented by the non-magnetic one-component developer. If the proportion of the free external additive particles exceeds 9% by number, such an excellent effect cannot be expected.
The above objects of the present invention are also achieved by a developing apparatus comprising:
a developing roller that transports the non-magnetic one-component developer of the present invention in a predetermined direction; and
a metal blade that faces the surface of the developing roller and restricts the non-magnetic one-component developer within a predetermined thickness.
With this developing apparatus, excellent image formation can be carried out without causing welding, even after a continuous image forming operation over a long period of time.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.